[Diy_efi] Is E85 worth it?

Daniel Nicoson A6intruder
Sat Aug 26 01:26:27 UTC 2006


I am curious of your source of the #4 passage below.  I think your science
is somewhat flawed.  I do agree that any normal engine will maximize it's
efficiency by configuring the engine to take advantage of the higher octane
available.  This usually means a higher compression ratio that will allow
better fuel efficiency.

I question the issue of not comparing the BTU in versus work out.  That is
how you determine efficiency, how much energy out versus the amount input.
You have to compare apples to apples.  I think what you really mean to say
is that the layman's measure of efficiency miles per gallon is really an
economic measure of work out (miles driven) per dollar input.

Actual thermodynamic efficiency would entail comparing the BTU input of the
fuel compared to the work output (converted to BTU for direct comparison).

For long term success in the marketplace, the "layman's efficiency" is what
will really count (it of course is determined by thermodynamic efficiency
and the price of various fuels).  The long term success of ethanol or any
other alternative fuel will boil down to its cost relative to good old

I curious what you mean by saying the ethanol will produce more gas
molecules with lower BTU input resulting in a higher pressure?  I think you
are trying to say that the ethanol is more powerful in an ICE with lower BTU
input?  That's just not true.

I do appreciate the clarification on the pipeline compatibility issue.  It
sounds like BP could have used a bunch of ethanol going through its
pipelines on the north slope of Alaska the last few years...

Take care,

Dan Nicoson

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of Klaus Allmendinger
Sent: Friday, August 25, 2006 5:58 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] Is E85 worth it?

4. Greenhouse gas production
The higher hydrogen/carbon ratio of ethanol or methanol means that a lot of
the energy is produced from the combustion of hydrogen vs carbon. This
lowers the tailpipe emissions of CO2 and CO dramatically for the same energy
unit. Also a comparison based purely on BTU (thermal) content as a basis for
milage prediction is unfair to these lower alcohols. As mentioned before,
they produce more gas molecules as combustion product and therefore higher
cylinder pressure with lower BTU input. After all, we are running internal
combustion engines, not steam engines, where a BTU comparison would be fair.
The lower flame-front temperatures of burning alcohol means also that less
nitrous oxides are produced.

Just my $0.02 worth.


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